Validates an agent's x402 v1 client implementation against a TunnelMind surface end-to-end. Two operating modes: - mode: "demo" — HMAC over a nonce against a publicly-published secret. Does not move USDC. Smoke proves the WIRE works, not money movement. - mode: "x402" — real Coinbase facilitator ...
Part of the TunnelMind Data API server.
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AI agents call x402_echo to retrieve information from TunnelMind Data API without modifying any data. This is common in research, monitoring, and reporting workflows where the agent needs context before taking action. Because read operations don't change state, they are generally safe to allow without restrictions -- but you may still want rate limits to control API costs.
Even though x402_echo only reads data, uncontrolled read access can leak sensitive information or rack up API costs. An agent caught in a retry loop could make thousands of calls per minute. A rate limit gives you a safety net without blocking legitimate use.
Read-only tools are safe to allow by default. No rate limit needed unless you want to control costs.
{
"version": "1",
"default": "deny",
"tools": {
"x402_echo": {}
}
}See the full TunnelMind Data API policy for all 54 tools.
These attack patterns abuse exactly the kind of access x402_echo gives an agent. Each links to the full case and the policy that stops it:
Other read tools across the catalogue. The same approach applies to each: allow, with a rate cap to control cost.
Validates an agent's x402 v1 client implementation against a TunnelMind surface end-to-end. Two operating modes: - mode: "demo" — HMAC over a nonce against a publicly-published secret. Does not move USDC. Smoke proves the WIRE works, not money movement. - mode: "x402" — real Coinbase facilitator dispatch (gated on operator wallet provisioning; currently returns "facilitator not configured"). Without an X-PAYMENT header, the endpoint returns HTTP 402 with a standards- compliant accepts[] array (USDC on Base, $0.001). With a valid X-PAYMENT header (base64-encoded payment payload), echoes the request body and returns an X-PAYMENT-RESPONSE settlement header. Use this tool when: - You are validating your agent's x402 v1 client implementation against a real public endpoint. - You want to demonstrate the full 402 → retry → settle wire end-to-end. Do NOT use this tool when: - You need a real paid operation — no TunnelMind production endpoint is gated behind x402 yet. Inputs: - X-PAYMENT (header, optional): base64(JSON) per the x402 v1 spec. Without it, a 402 challenge is returned. - Request body (optional): any JSON object to be echoed back on successful payment. Returns: - On no header: HTTP 402 + { x402Version, accepts: [...] }. - On valid payment: HTTP 200 + { ok: true, data: { echoed, paid_micro_usdc, x402 } } and an X-PAYMENT-RESPONSE header carrying the settlement record. - On invalid payment: HTTP 402 + { error: "invalid payment", reason }. Discovery: - https://tunnelmind.ai/.well-known/x402.json carries the public demo secret and the HMAC construction recipe. Cost: - Free in demo mode (no USDC moved). $0.001 USDC in real-mode (when activated). Latency: - Typical <100ms (demo mode); real mode is bounded by facilitator latency.. It is categorised as a Read tool in the TunnelMind Data API MCP Server, which means it retrieves data without modifying state.
Register the TunnelMind Data API MCP server in PolicyLayer and add a rule for x402_echo: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches TunnelMind Data API. Nothing to install.
x402_echo is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the x402_echo rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for x402_echo. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
x402_echo is provided by the TunnelMind Data API MCP server (https://mcp-data.tunnelmind.ai/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 54 TunnelMind Data API tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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